When I return from the woods after a walk with the dogs, I run my hand across their fur—and the palm of my black glove comes back white. When I inadvertently touch my face, I taste—salt.
But my dogs don’t walk in the street—just in the woods, in the snow. So the white on their coats comes from the road salt that is aerosolized in the air in my car and around the woods.
The dogs and I can, of course, counteract the effect of all this excess salt by drinking water, which they do, I notice, in copious amounts.
But what about when all that salt washes into our sewer drains, and then into our rivers and oceans, and even just into the soil by the roadside? And what about when it permeates our aquifers — and our lungs?
As I drive on the highway, I notice cars encased in a white crust: we can wash our cars but—what about our lungs? I wonder if the pathologists, who used to like to horrify medical students with slides of the average city dweller’s black lung due to all the pollution he inhales are now showing off—white lung.
What is in road salt? In addition to sodium chloride (table salt), it usually contains other chloride salts such as magnesium chloride, calcium, and potassium chloride; ammonium nitrate, ammonium sulfate, sodium acetate and calcium magnesium acetate may also be added to the mix, as well as some basic salts such as calcium hydroxide. But of course, add water, and these salts can recombine into magnesium sulfate (fertilizer) and sodium hydroxide (corrosive).
Those salts corrode our cars and our roadways. Never have I seen so many potholes—entire roads appear to be disintegrating this year. It would be helpful to determine the role that the uneven distribution of freezing stress on the road due to excessive salting may be playing—and one that cities and towns would be wise to study. This is a very expensive side effect.
What about when it seeps through to the infrastructure below the street, corroding our aging cast iron gas pipelines? How much is all of this salt contributing to the thousands of methane gas leaks we see in and around Boston?
Are there other expensive side effects on human health? I find myself wondering about the effect on small children, and the runners preparing for the Marathon—they aren’t in the woods, they are right on top of the salt in the streets and sidewalks. What are they inhaling other than salt?
Heavy metals, for one. Lead and mercury mingle with road salt and are found to be present in the winter at levels twice to three times what they are in the summer months, according to a 2017 article in Water Science Technology; in that study, German researchers found that “heavy metal concentrations with salt doubled and tripled median concentrations for heavy metals during the cold season.” And a study in Scandinavia showed that “the contribution of road salt to PM10 concentrations can be significant if dry residual salt is left on the road after deicing is carried out.” In fact, “non-exhaust traffic emissions”–ie road salt–”are a major source of airborne particulate matter.” Contributions of salt vary but during winter months this can range from 10% to 35% of the average PM10 concentration—the most significant contributor to this pollutant other than automobile exhaust.
How much of that lead and mercury gets into the mouths and lungs of young children and outdoor enthusiasts? And car drivers, for that matter? Wouldn’t that be good to know?
Also–a lot of this road salt is mixed with petrochemicals–in fact in many parts of the country, road salt “brine” is waste from petrochemical extraction like fracking–and so is contaminated with benzene, toluene and radioactive waste like radium. This is supplied for free(!), according to this Newsweek article, to many communities–companies are happy not to have to pay for disposal.
I am all for road safety. But there are no good studies showing that increased salt use has decreased accidents or fatalities. A quick Google search reveals a study cited in 2017 as if it happened yesterday: but they are in fact referring to a 1992 study showing that salt “reduces road deaths by 88%.” You will also see entries from the Salt institute saying “don’t you feel safe, seeing the Salt truck?”
But should you feel safe?
First, the 1992 Marquette University study (actually, a graduate student thesis), funded by the Salt Institute, had no control group, meaning it is not possible to tell what would have happened without any intervention at all, with plowing alone, with sanding without salt. Sanding plus salt, the study reports, had no effect (and in the corner of the graph it reads mysteriously—Mild Winter. So the salt part of the story happened in a different winter?).
On the other hand, many excellent studies show that the wide scale adoption of road salt in this country is leading to environmental and human health impacts that fly under the radar for most people.
Interestingly, the same university in Wisconsin that produced that study is now looking for grant money to study the northern lakes that have dead zones due to excessive salt use on the roads—because salt acts as a potent fertilizer, making nasty cyanobacteria (commonly but incorrectly known as blue green algae) grow avidly. And the cyanobacteria kill fish by starving the water of oxygen –and make water unswimmable in the summer.
According to Rick Relyea, a professor of biological sciences at Tensselaer Polytechnic, salt also degrades the soil by killing the bacteria that hold the soil together, leading to soil erosion; it also makes the environment more vulnerable to invasive species.
When it gets into the water supply—it is contaminating aquifers and private wells alike, as well as streams and lakes, as reported in this article in the Atlantic: it can make the plumbing corrode, causing the lead solder to dissolve in the water—leading to elevated lead levels. Excessive road salting is blamed for the lead crisis in Flint, Michigan. It is making vast swaths of water across the world undrinkable.
I notice the salt islands, collecting on the sidewalks and streets.
And then I notice something else—when I travel to Cambridge and Brookline, I don’t see them. There are no mountains of salt on the sidewalks and next to the curb; the streets aren’t coated in a film of white, obscuring the markings on the street. And yet there doesn’t seem to be any greater difficulty in getting around.
When I arrived here in Massachusetts a little over 20 years ago, this love affair with salt was yet to begin. On the street corners, one would find partially overturned trashcans with sand in them during the winter for those who found themselves in need of a little extra traction on a hill or by the school. The schools sanded the walks in front—and it seemed to work perfectly well. Now there is only– salt.
What about the impact on trees? “We really have no recourse if we undermine the life upon which our life rests,” said Harvard School of Public Health Professor Dr. Ari Bernstein in a talk on Climate and Health at the BU School of Public Health.
If we lose those trees, we can expect hotter summers and colder winters, because trees act as an insulating blanket on the earth, mitigating the extremes of hot and cold. This in addition to losing the Gulf Stream due to the dilutional effect of the melting of the Arctic ice sheet, could mean much colder temperatures in the Northeast and in Europe, which owe their habitability to that Gulf stream.
So although it may not seem to matter much to see the salt burns on the grass along Commonwealth Avenue when the snow melts back in the spring— to the extent that it is also killing the trees—it very much does. We often do, I think, forget that our life depends on the oxygen production of trees. Look at the ones around your house. Which ones would you trust your life to? All the trees in my neighborhood are looking very stressed—rotting off branches, sick green slime, listing in impossible positions due to stress. “We really have no recourse if we undermine the life upon which our life rests.”
There are now better alternatives to salt: according to this article in Smithsonian, superior plows that have curved blades that do a better job of clearing the road. Sand doesn’t pollute the water we drink and doesn’t kill wildlife like moose, fish and frogs that are being done in by roadway salt.
According to Relyea: “We’ve been dramatically increasing the amount of salt per mile since the 1970s, even in places where we don’t need it. The answer isn’t really in alternative salts but in less salt.”
So next time we think about “treating” our driveways or roads—try sand. You may save your health, or that of your dog, or child, the nearby lake, the drinking water of the next town.
Not to mention the trees–that “life upon which our life depends.” We are undermining so much life with no evidence that we are saving ours.
More Resources:
Blue green green algae that are tied to excess road salt–which starves the water of oxygen:
“Brine can be as much as 10 times saltier than typical road salt. Plus it comes cheap; oil and gas companies, glad not to have to pay for disposal, will sell it to towns for cheap, or give it away free.” https://www.newsweek.com/oil-and-gas-wastewater-used-de-ice-roads-new-york-and-pennsylvania-little-310684
Levels of radioactive material found in conventional brine samples taken from New York are equal to levels he has seen in fracking brine:
https://www.wateronline.com/doc/salt-in-produced-water-might-harmful-when-used-icing-roads-0001
Road salt applications is linked to increased radioactive radium in water supplies:
https://pubs.acs.org/doi/full/10.1021/acsestwater.1c00307
“Chloride is toxic to aquatic life, and even low concentrations can produce harmful effects in freshwater ecosystems. Runoff containing road salt can also cause oxygen depletion in bodies of water. “If runoff containing salt goes into a freshwater lake or stream, it will tend to sink towards the bottom, creating a dense layer that can inhibit gas exchange with the overlying water,” says Juhl. “This can lead to the development of low oxygen conditions that are detrimental to fish and other aquatic organisms.”
https://news.climate.columbia.edu/2018/12/11/road-salt-harms-environment/
“Salt is also corrosive, as many car owners can attest. But salt eats away at more than just auto bodies – it corrodes roads, bridges and other infrastructure. It’s been estimated that damage from salt corrosion alone may cost the U.S. as much as $5 billion a year. In 2015, Flint, Michigan’s municipal water supply was found to be contaminated with high levels of lead, a neurotoxin. Researchers linked this contamination to high chloride levels in Flint’s water, which had corroded lead pipes throughout the city’s plumbing system. A primary suspect behind the elevated chloride levels in Flint’s water? Road salt.
Some 13 states in the U.S. allow salty wastewater from oil and gas production wells to be spread on roadways. However, studies have found that these wastewater brines can contain toxic elements including radium, a carcinogen, and that these contaminants could accumulate in soil and groundwater or even become airborne.”
Across the U.S. road crews dump around 25 million metric tons of sodium chloride:
https://www.sciencedaily.com/releases/2021/12/211209124519.htm
